1. Field of the Invention
The present invention relates to labels used in in-mold forming. The present invention further relates to molded resin products to which such labels are applied.
2. Discussion of the Background
In-mold forming is a known method of manufacturing labeled molded resin products by integrated molding. In this method, a label is placed in advance on the inner wall of a mold, a moldable resin such as polyethylene or propylene based resin is melted and directly fed into the mold, and the label is attached by injection, vacuum, differential pressure, or foam molding (see Japanese Unexamined Patent Publication (KOKAI) Showa No. 58-69015 and European Patent Publication No. 254923). Known forms of such labels used in in-mold forming are gravure printed resin films, polychromatic offset printed synthetic paper (for example, see Japanese Examined Patent Publication (KOKOKU) Heisei No. 2-7814 and Japanese Unexamined Patent Publication (KOKAI) Heisei No. 2-84319), and aluminum labels comprising aluminum foil on the rear side of which is laminated a high-pressure low-density polyethylene or an ethylene-vinyl acetate copolymer and on the front side of which gravure printing is conducted.
However, in the manufacturing of labeled containers by hollow molding using these conventional in-mold forming labels, when the portion of the container to which the labels are attached is highly curved or undulated, there is a problem during expansion of the parison being extruded from the die by the injection of air in that air present between the label secured in the mold and the parison forms air pockets known as “blisters.” Since labeled containers having blisters are of little commercial value, there is a need to prevent blister formation.
In response to such problems, Japanese Examined Patent Publication (KOKOKU) Heisei No. 6-70736 and Japanese Examined Utility Model Publication (JIKKO) Heisei No. 7-54109 propose that special through-holes be provided in the label to suppress blistering.
However, when the shape of the container involved is cylindrical (meaning containers designed to have true circular cross-sections when viewed from the top or bottom, including the case where there is some deviation from a true circular form due to dimensional error in the mold, contraction of resin in the mold, or the like), as shown in the sectional view of FIG. 1, when label (1) occupies a large amount of the area along the perimeter of container (2), preventing blistering necessitates either providing large-diameter through-holes or increasing the number of through-holes per unit area to facilitate the escape of air. However, when large-diameter holes are made, labeled containers of poor appearance due to conspicuous through-holes are obtained. When the number of through-holes per unit area is increased, due to the presence of numerous through-holes in the label in the area of the suction pad (normally about 10 to 30 mm in diameter) of the automatic label feeder, problems are encountered in the course of picking up stacked labels in that the labels cannot be picked up by suction, the labels fall off along the way, or two labels are picked up at once. There are also problems in that, depending on the size and positioning of suction holes in the mold in which the label is secured, the label cannot be secured in the proper position.
To minimize these problems, it is necessary to form suitable through-holes in the label by trial and error in combining the shape of the container and label, the size and positioning of the suction pads, and the size and positioning of the suction holes in the mold. Thus, for conventional labels, it has not been possible to widely employ various container and label shapes, or the broad use thereof has not been possible with feeding units and molds.
Japanese Examined Patent Publication (KOKOKU) Heisei No. 4-71699 proposes the prevention of blistering by the use of a film having minute ventilation holes. However, when ventilation is increased excessively to prevent blistering, the above-described problems with label feeding with an automatic label feeder tend to occur. Thus, this label is also precluded from use in various shapes on a variety of differently shaped containers, or is precluded from wide use in feeders and molds.
In light of the above-described problems of prior art, the object of the present invention is to provide a label for in-mold forming permitting the attachment of labels while effectively inhibiting blistering on molded resin articles having a variety of shapes. A further object of the present invention is to provide a label for in-mold forming permitting smooth suction by automatic label feeding devices and reliable securing of labels, thereby affording high manufacturing efficiency with in-mold labels. A still further object of the present invention is to provide a labeled molded resin article that is attractive in appearance and can be manufactured economically.